Coronary heart disease, atherosclerosis, is the leading cause of human mortality in the United States, as well as in many other developed countries, and is responsible for more deaths than all forms of cancer combined. It is generally recognized that high blood cholesterol concentrations provide a significant risk factor associated with atherosclerosis.
Cholesterol is present in the blood as free and esterified cholesterol within lipoprotein particles, commonly known as chylomicrons, very low density lipoproteins, low density lipoproteins and high density lipoproteins. Concentration of total cholesterol in the blood is influenced by (1) absorption of cholesterol from the digestive tract, (2) synthesis of cholesterol from dietary constituents such as carbohydrates, proteins, fats and ethanol, and (3) removal of cholesterol from blood by tissues, especially the liver, and subsequent conversion of the cholesterol to bile acids, steroid hormones, and biliary cholesterol. The bile acids and cholesterol in bile are secreted into the intestine from which they may be recycled back to the blood or be excreted into the feces. In summation of these physiological processes, the concentration of cholesterol in the blood is controlled by a balance of inputs and outputs. The two inputs are cholesterol absorbed from the diet and cholesterol that is synthesized within the body and secreted into the blood. Typical values of adult humans for absorption are 335 mg daily and for synthesis are 800 mg.
The outputs regulating the concentration of cholesterol in blood include sloughing skin cells (about 85 mg cholesterol daily), excretion of steroid hormones (about 50 mg cholesterol daily), excretion of bile acids in feces (400 mg cholesterol equivalent daily), and excretion of sterols in feces (600 mg cholesterol equivalent daily). The fecal sterols include cholesterol, cholestanol, coprostanol, and plant sterols. The whole body of the adult human contains about 100 grams of cholesterol, most of which is in the nonesterfied form.
Maintenance of blood cholesterol concentrations is influenced by both genetic and environmental factors. Genetic factors include concentration of rate-limiting enzymes in cholesterol biosynthesis, concentration of receptors for low density lipoproteins in the liver, concentration of rate-limiting enzymes for conversion of cholesterols bile acids, rates of synthesis and secretion of lipoproteins and gender of person. Environmental factors influencing the hemostasis of blood cholesterol concentration in humans include dietary composition, incidence of smoking, physical activity, and use of a variety of pharmaceutical agents. Dietary variables include amount and type of fat (saturated and polyunsaturated fatty acids), amount of cholesterol, amount and type of fiber, and perhaps amounts of vitamins such as vitamin C and D and minerals such as calcium.
Pharmaceutical agents in current use that usually cause a hypocholesterolemic response include lovastatin, which decreases cholesterol synthesis in the body, and cholestyramine, which increases bile acid excretion. An increase in bile acid excretion causes the liver of the person to convert more cholesterol to bile acids and to incorporate less cholesterol in very low density and low density lipoproteins for secretion into the blood. Hence, cholestyramine usually causes a hypocholesterolemic response.
Similar to that for bile acid excretion, increases in the excretion of cholesterol and other sterols into the feces usually will cause a hypocholesterolemic response because the liver would partition more cholesterol into the bile and thus less would be available for incorporation into lipoproteins for secretion into the blood. Typically, a human secretes about 1,000 mg of cholesterol from the liver into the bile for entry into the small intestine. This biliary cholesterol then becomes a part of the dietary cholesterol pool in the small intestine and thus may be absorbed to maintain cholesterol homeostasis.
The present invention discloses a method and means for decreasing the amount of biliary and dietary cholesterol that is absorbed by the small intestine through oral administration of coprostanol-producing microorganisms. Several species of bacteria including Eubacterium coprostanoligenes (previously called Eubacterium sp. strain HL by us) isolated in pure culture from an Iowa State University hog lagoon (ATCC No. 21408) contain the enzyme cholesterol reductase. These bacteria, which produce this enzyme, are capable of converting cholesterol to coprostanol. The resultant coprostanol product is absorbed poorly by humans and, instead of being absorbed through the intestine into the blood, will be passed through the intestine and excreted in the feces of the human.
Thus, an objective of the present invention is to decrease cholesterol absorption in the small intestine through administration of coprostanol-producing microorganisms.
Another object of the invention is to convert cholesterol present in the small intestine to coprostanol, which will be excreted.
Yet another objective of the invention is to lower plasma concentration of cholesterol in humans by generating a hypocholesterolemic response resulting in partitioning by the liver of more cholesterol into bile with less available for incorporation into lipoproteins for secretion into the blood.
Another objective of the present invention is to provide a pharmaceutical composition for oral administration, which will release the coprostanol-producing organisms in the small intestine of humans.